Apparatus for developing electrostatic printing



June 26, 1962 w. H. BLISS 3,040,704

APPARATUS FOR DEVELOPING ELECTROSTATIC PRINTING Var/16E sou/16E 9 IN VEN TOR.

Mmm lidu BY E i Warren H. Bliss,

United states Patent o 3,040,704 APPARATUS FOR DEVELOPING ELECTRO-STATIC PRINTING Princeton, NJ., assignor to Radio Corporation ofAmerica, a corporation of Delaware Filed Apr. 16, 1957, Ser. No. 653,1308 Claims. (Cl. 118-637) This invention relates to electrostaticprinting, and more particularly toan improved apparatus for applyingdeveloper powder to a record, such as a continuously moving web, bearingan electrostatic charge image.

A typical electrostatic printing process may include first producing auniform electrostatic charge upon the surface of -a photoconductiveinsulating material carried on one surface of a record. Then the chargedsurface of the photoconductive material is exposed to a light imagethrough a photographic transparency or by other suitable means. Theportions of the surface irradiated by the light rays become dischargedwhile the remainder of the surface remains in a charged condition,thereby Iforming a latent electrostatic image corresponding to the lightimage. The latent electrostatic image is developed `by applying acolored, electroscopic powder which is held electrostatically toselected areas of the surface. The visi-ble powder image thus formedmaybe fixed directly to the photoconductive surface by fusing.

An object of this invention is to provide an improved i apparatus forapplying a continuously moving record.

Another object of this yinvention is to provide an improved apparatusfor `applying developer powder, rnixed with magnetic particles, to thesurface of a continuously moving record.

A further object of this invention is to provide an improved apparatusfor presenting a continuous supply of freshly mixed developer powder andmagnetic particles to the surface of a continuously moving record.

A still further object of improved apparatus for mixing developer powderand magnetic particles and for presenting a continuous supply of mix toa continuously moving record.

In accordance with the present'invention, a developer mix comprising anelectroscopic developer powder and magnetizable carrier particles isapplied to a surface bearing a charge image in the presence of amagnetic field. A cylindrical drum is rotatably supported adjacent acon-V tainer lfor the developer mix. A non-rotating magnetic fieldproducing structure is supported lwithin the drum. A magnetic shuntmeans is associated with the field producing structure and reduces themagnetic field passing through a portion of the drum. A record bearing acharge image is directed adjacent a portion of the drum surface.

By means of the magnetic field, the developer mix is.

caused to adhere tothe drurn'surface and is carried from the containerto the record. Certain of the developer powder is electrostatically`attracted to the record. The developer mix remaining on the drum isthen caused to drop from the drum surface because of the reducedmagnetic field.

rIhe novel features of the invention, as well as addi' tional objectsand advantages thereof, will be understood more fully from the followingdescription wheny read in connection with the accompanying drawing, inwhich:

FIGURE l is a diagrammatic view illustrating an electrostatic printingsystem embodying the present invention;

FIGURE away, of one embodiment FIGURE 3 is a sectional 2 is a view inelevation, partially breiten of the present invention; view taken alongthe line 3--3 developer powder to the surface of this' invention is toprovide an 3,040,704 Patented June 26, 1962 2 of FIGURE 2 looking in thedirection of the appended arrows; t

FIGURE 4 is a fragmentary end view of the magnetic field producing meansof FIGURE 3 and its supporting structure;

FIGURE 5 is a sectional view, similar in part to FIG- URE 3,illustrating the magnetic field distribution;

FIGURE 6 is la View, Similar to FIGURE 3, illustrating lanotherembodiment of a magnetic field producing structure of the presentinvention; and

FIGURE 7 is a'view' similar to FIGURE 3jillustrating still anotherembodiment off a magnetic field producing structure of the presentinvention.

The apparatus to tbe described, embodying the invention in illustrativeforms, may be operated with a developer mix comprising an electroscopicdeveloper powder and a carrier material consisting of magnetic particlessuch as alcoholized iron. Generally, any of a large number of developerpowders, known in the art, is suitable for mixing with iron particles toform a developer mix to be employed in operatingy the present invention.A developer powder above iron in 4the triboelectric series is generallysuitable for developing a direct image uponV a negatively chargedsurface, or a reverse image upon a positively charged, surface. Forpurposes of illustration there is described herein, by way of example,the development of aV direct image upon a negatively charged surface.Reference will be had to a record receiving member 11, in the form of apaper sheet or web, having a photoconductive coating which' may comprisezinc oxide dispersed in an electrically-insulating film-forming vehicle,such as resin.

Referring now to FIGURE 1 of the drawing, an electrostatic prntingsystem is shown diagrammatically. A continuous web 11 is fed from asupply spool 13 and is pro'- vided with a photoconductive coating on itslower surface as it is fed from the spool. The photoconductive surfaceis exposed to the influence of an electrostatic charging device 15 toprovide a distributed electric charge over the surface. Ihe chargingdevice 15 may comprise a plurality of fine wires `17 carried by a pairof spaced insulating members. It will be understood that the insulatingmembers are spaced in such a manner that the wires 17 span the widtho-fthe web 11. Light is preferably excluded during the charging step. Asource of high voltage 19 is connected to the wires 17 so as to providethe wires with a negative charge with respect to a ground plate 21.

The charged web is next exposed to a light image from a luminous imageprojector of any known kind. The web ynow bears a latent image in theyform of an electrostatic charge. The web next passes overa roller 25 toa developer powder applying apparatus 27 which will be described indetail hereinafter. The web next passes over a roller 29 which guidesthe web so that it is drawn past a heater or fuser 31 where thedeveloper powder is fixed to the web surface to form 4a permanent image.The web is drawn through the various stages of the system by means of afeed roller 33 `and an -associated pressure roller 35. The lfeed roller33 may be driven by an electric motor 37 of -any suitable type.

Referring now particularly to FIGURES 2 through 5, one embodiment of theaforementioned developer powder applying4 apparatus 27 will be describedin detail. A

container, in the form of a rectangular trough 41, is prois open at thetop. A mag- 3 43 is joined to the flat face of the semicylinder by meansof brazing or soldering, for example. The bar 43 is provided wit-hjournal shafts 47 and 49 at either end. The shafts are offset from theface of the bar 43 so as to coincide with the axis of the semicylinder45.

The above described eid producing structure is supported by means of thejournal shafts 47 and 49. The shaft 47 is secured in one end of thetrough 41 and fixed against rotation so that the field producingstructure remains fixed with respect to the trough.

A hollow `cylindrical drum 51, of a non-magnetic material, encloses theabove described field producing structure and has an internal diameterslightly larger than the diameter of the semicylindrical magnet 45. Thedrum 51 is mounted for rotation -about the journal shafts 47 and 49. Abearing member 53 is secured to one end of the drum S1. The bearingmember 53 includes a drum for supporting an internal bearing 55 forengagement with the journal shaft 49 of the bar 43. The bearing member53 also provides a journal shaft for association with a lbearing 57mounted in the other end wall of the trough 41. The shaft of the member53 is coupled to a suitable driving source, such as a motor 59 of anyknown type.

In the manner above described, the magnetic field producing structureand the drum 41 are concentrically supported in the trough, the drum 51being rotatable about and completely enclosing the field producingstructure.

Referring now particularly to FIGURES 3 and `5, it will be seen that themagnet bar 45 is magnetized to produce a field perpendicular to itslongitudinal axis, the two magnetic poles lying along the opposite edgesof the. fiat face of the bar 45. With this arrangement, the fielddistribution should appear Aapproximately as is shown in FIG- URE 5 ofthe drawing. The flux lines shown in the left hand portion of FIGURESpass through the drum 51 and form a return path in air. The rectangularbar 43, which is secured to the flat face of the bar 45, -acts as amagnetic shunt and distorts the field distribution as shown in the righthand portion of FIGURE 5. A substantial portion of the iiux lines passthrough the bar 43 to substantially reduce the strength of the magneticfield passing through the drum on this side of the magnetic structure.As a result of this structure, magnetic particles adhere to kthe drum onthe left side of the structure, as shown in FIGURE 5, and `do not adhereto the drum on the right hand of the structure, `as shown in FIGURE 5.

An elongated shoe 61 of non-magnetic material is supported over thetrough 41 by means of brackets 63. The shoe has a rounded face opposingthe surface of the drum 51 and is spaced from the drum surface so that,as the web 11 is guided over the shoe, the developer mix held to thesurface of the drum 51 will engage the charged surface of the web 11.

In operation, the trough 41 is filled with a `developer mix, as abovedescribed, to a level somewhat above the lower surface of the drum 51.The web is fed between the shoe 61 and the drum 51 in a manner shown anddescribed, and is carrying a latent charge image on its lower surface atthis stage of the operation. Referring now to FIGURE 3, the drum 51 isrotated in a clockwise direction by the motor S9 and the web 11 is drawnpast the `shoe in a -direction from right to left. In this manner thedirection of motion of the web11 and the drum 51 are opposite at thetransfer area. As the drum is rotated, the developer mix is attractedfrom the trough to the drum, which preferably has a roughened externalsurface, and the mixture adheres to the drum in the form of bristles.The bristles may tend to lie flat as they are carried past the left sideof the magnetic structure (FIGURE 3) due to the configuration of themagnetic field. However, as the drum carries the mix toward the top ofthe structure, the bristles again become erect due to the configurationof the magnetic field. At .the top of the magnetic structure, thebristles engage the surface of the web 11 and,

- 4 due to electrostatic attraction, the developer powder particles areattracted from the bristles to the charged areas of the web. Themagnetic particles of the mix are not attracted to the web.

As the drum carries the remaining developer mix, which now compriseslargely the magnetic particles, past the top of the magnetic structuretoward the right hand side thereof, the bristles collapse and theremaining mix falls, by gravity, back into the trough 41 due to thereduced magnetic field. As the drum rotates then, the forming, carrying,collapsing, and falling of the bristles of developer mix tend to mix thedeveloper powder and magnetic particles. It will be apparent that freshdeveloper powder must be continuously supplied to the trough to providefor a continuous operation. Since the magnetic particles remain in thesystem, it is not necessary to replenish them.

Referring now to FIGURE 6 of the drawing, another embodiment of a fieldproducing structure will be described. The structure of trough 41, thedrum 51, and the shoe 61 are as described above. In this form, however,the shoe 61 is made of a magnetic material. A semicylindrical magnet 55is the same as that previously described. A non-magneticsupporting bar71, also semicylindrical in cross-section, is secured to the fiat faceof the magnet bar 55 and may be provided with journal shafts similar tothose described for the bar 43. The diameter of the bar 71 is smallerthan that of the magnet bar 55 and a semicylindrical sleeve member 73 issecured to the cylindrical surface of the bar 71. The sleeve 73 is madeof a magnetic material, such as soft iron, and acts as a magnetic shuntin a manner similar to that of the bar 43 to reduce the magnetic fieldat the right hand portion of the structure. The structure consisting ofthe magnet bar 55, the support bar 71, and the sleeve 73 then forms acompletely cylindrical structure enclosed by the ldrum 51.

The shoe 61 is of a magnetic material which tends to t confine andstrengthen the magnetic field in the transfer area. As `a result of thisthe bristles of the developer mix may be stiffer as they are presentedto the surface of the web 11. The operation of this embodiment of theinvention is the same as that of the first described embodiment.

Referring now to FIGURE 7 of the drawing, still another embodiment ofthe invention will be described. The trough 41 and the drum S1 are lasdescribed heretofore. The magnetic eld is produced by a cylindricalmagnet supported in a manner similar to the field producing structure`described above and polarized in a direction transverse to itslongitudinal axis. A semicylindrical sleeve 73, of a magnetic material,is Isecured to and enclos'es the right hand half of the magnet 81. Thesleeve 73 again acts as a magnetic shunt to reduce the magnetic field inthis portion as described above. The shoe 61 has a configurationsubstantially as described above and is made of a non-magnetic material.The shoe is provided with a longitudinal groove located opposite fromthe rounded surface at the transfer area of the structure. An elongatedbar magnet 83 is secured in this groove and is polarized in a directionperpendicular to its longitudinal dimension. The pole nearest thetransfer area is of a polarity opposite from the pole of the cylindricalmagnet 81 nearest the 4transfer area.

This structure is provided to again further strengthen the magneticfield in the transfer area so as to increase the stiffness of thebristles of the developer Care must be taken to insure that the fieldprovided by the magnet 83 is not so strong as to cause the magneticparticles of the developer mix to be `attracted to, and to adhere to,the surface of the web 11. i

A significant feature of the above described embodiment of the inventionis the structural simplicity of the apparatus for providing continuousdevelopment of ya moving web. Another significant and important featureof the apparatus is the fact that the magnetic field producing structureis completely enclosed in a non-magnetic drum. With this structure thereis little tendency -for the magnetic particles to collect in areas wherethey serve no useful purpose and where they may interfere with theoperation of various parts of the mechanism.

What is claimed is: A

l. Apparatus for developing a latent electrostatic charge image on arecord rreceiving member comprising means for driving and moving arecord receiving member bearing a latent electrostatic charge image, acontainer for a developer mix comprising electroscopic developer powderparticles and magnetic particles, a magnetic eld producing structurerigidly supported in said container, a cylindrical drum of non-magneticmaterial rotatably mounted in said container and enclosing said magneticiield producing structure, said field producing structure producing aiield which passes through said drum, means associated with said iieldproducing structure for reducing the magnetic iield passing through aportion of said drum, means for guiding said record receiving memberadjacent said drum, and means for rotating said drum to carry saiddeveloper -mix vfrom said container to said record.

2. Apparatus for developing a latent electrostatic charge image on -arecord receiving member comprising means for driving and moving a recordreceiving member bearing `latent electrostatic charge image, a troughfor containing a developer mix comprising electroscopic developer powderparticles `and magnetic carrier particles, a magnetic iield producingstructure rigidlysupported in saidv trough, a cylindrical drum'ofnon-magnetic material rotatably mounted in said trough andenclosing saidmagnetic iield producing structure, drive means for said drum, saidfield producing structure producing a field acting in a directiontransverse to the rotational axis of said drum land passing through saiddrum to cause said developer -Inix to adhere to the surface of saidd-rum, means for reducing the magnetic field produced by said iieldproducing structure over a portion of said drum to effect the release ofsaid mix from said drum surface, and means for guiding said recordreceiving member adjacent said drum to effect the transfer of saiddeveloper powder from said drum to said record receiving member.

3. Apparatus for developing `a latent electrostatic 4charge image on a4record receiving member comprising means for driving and moving `arecord receiving member bearing a latent electrostatic charge image, atrough for containing `a developer mix comprising electroscopicdeveloper powder particles and magnetic carrier particles, `a

magnetic field producing structure rigidly supported in' said trough`and extending longitudinally thereof, a closed cylindrical drum ofnon-magnetic material rotatably mounted in said trough and enclosingsaid magnetic iield producing structure, said field producing structureproducing Va field acting ina direction transverse to the rotationalaxis of saiddrum to cause sai-d developer mix to be attracted to thesurface of said drum and to be maintained on said drum in a bristle-likeformation, meansvfor reducing the magnetic field produced by said iieldyproducing structure over a portion of said drum to effect the release ofsaid developer mix from said drum surface, and means for guiding saidrecord receiving member adjacent said drum, and means for driving saiddrum whereby said developer mix is carried from said trough intoengagement with said record receiving member and released to saidtrough.

4. Apparatus for depositing electroscopic developer powder lfrom amixture of such powder and a quantity of magnetic particles `onto a.member bearing an Ielectrostatic charge image, said apparatus comprisingmeans Iforsupporting and advancing a member bearing an electrostaticcharge image, a rotatably mounted cylindrical drum, a non-rotatablefield producing means supported within said drum, said magnetic fieldproducing means producing a 'field which passes through the cylindricalwall of said drum to cause said mixture to adhere to said drum in theform of bristles, means associated with said magnetic eld producingvmeans for reducing said magnetic field passing transfer of saidelectroscopic `developer powder from said drum to said member.

5.v Apparatus for depositing electroscopic developer powder from amixture of such powder and a quantity of magnetic particles onto amember bearing an electrostatic charge image, said apparatus comprisingmeans for supporting and advancing a member bearing an electrostaticcharge image, a rotatably mounted cylindrical drum, a non-rotatableiield producing means supported within said drum, said magnetic fieldproducing means producing a lieldwhich passes through the cylindricalwall of said drum to cause said mix to adhere to said wall in the formof bristles, means associated with said magnetic eld producing means forreducing said magnetic eld passing through la portion .of the path ofsaid cylindrical drum wall to effect the release ofsaid magnetizableparticles from said wall, means for providing, a quantity of thedeveloper mixture adjacent to said drum wall, and means for directingsaid member bearing an electrostatic charge image adjacent said drum,and means for rotating said drum to carry said mixture to said member toeffect transfer of said electroscopic developer powder from said drum tosaid member.

6. Apparatus for depositing electroscopic developerV powder from amixture of such powder and a quantity of magnetic particles onto amember bearing an electrostatic charge image, said apparatus comprisingmeans for supporting and advancing a member bearing an electrostaticcharge image, a rotatably mounted cylindrical drum, a non-rotatable ieldproducing means supported within said drum, said field producing meanscomprising a semicylindrical magnetized bar polarized in a directiontransverse to its axis, said'bar producing a field which passes throughthe cylindrical wall of said drum to cause said mixture to adhereV tosaid drum in the form of bristles, a

magnetic member associated with said magnetized bar for shunting aportion of the magnetic field to effect the release of said magnetizableparticles from said drum wall, means for introducing a quantity of saiddeveloper mixture to said drum, and means for directing said memberbearing an electrostatic charge image adjacent said Y drum, and meansfor rotating said drum to carry said mixture to said member to eiiecttransfer of said electroscopic developer powder from said drum to saidmember.

7. Apparatus for depositing electroscopic developer pow-der from amixture of such powder and a quantity of magnetic particles onto amember bearing'an electrostatic charge image, said apparatus comprisingmeans for sup porting and advancing a member bearing an electrostaticcharge image, a rotatably mounted cylindrical drum, a cylindricalmagnetized bar completely enclosed by said drum, means for supportingsaid har against rotation, said bar being polarized in a directionperpendicular to its longitudinal axis to produce a magnetic field whichpasses through the cylindrical wall of said drum to cause said mixtureto adhere to said drum in the form of bristles, a semi-cylindricalmagnetic shield associated with said har, said shield acting as amagnetic shunt to reduce the magnetic field passing through a portion ofsaid drum wall to eifect the release of said mixture from said drumwall, means for introducing a quantity of developer mix to said drum,means for directing said member bearing an electrostatic charge adjacentsaid drum, and means for rotating said drum to carry said mixture tosaid member to eiiect transfer of said electroscopic developer powderfrom said drum to said member. y

8. Apparatus for developing a latent electrostatic charge image on arecord receiving member comprising means for driving and moving a recordreceiving member hearing a latent electrostatic charge image, acontainer for a developer mix comprising electroscopic developer powderparticles and magnetic particles, a magnetic field producing structurerigidly supported in said container,

Ya cylindrical drum of non-magnetic material rotatably mounted in saidcontainer and enclosing said magnetic field producingstructure, meansfor 'guiding said record receiving member adjacent said drum, and meansfor rotating said `drum to carry said developer mix from said containerto said record, said magnetic eld producing structure producing a fieldwhich passes through only that portion of said drum which carries saiddeveloper mix from said container to said record, leaving the portion ofsaid drum, during the rotation thereof, which has passed said recordsubstantially devoid of said magnetic eld so that the developer mixthereon is no longer held by magnetic attraction and is discharged fromsaid latter portion into the developer mix in said container.

References Cited in the lle` of this patent UNITED STATES PATENTS1,714,171 Iobke May 21, 1929 2,634,861 Stearns n Apr. 14, 19532,703,175` Becking Mar. 1, 1955 2,786,440 Giaimo Mar, 26, 1957 2,791,949y Simmons et al 27.* May 14, 1957

